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Praxair Cryogenic Supply Systems: An Inside Look

Commitment to Cryogenic Excellence

Praxair designs, installs and maintains its cryogenic systems to provide a reliable, consistent supply ofargon, hydrogen, nitrogen, and oxygen. Our goal is to provide 100 percent supply reliability at theappropriate purity and pressure required. To help us meet this goal, we regularly monitor the supplysystem through a combination of real-time remote monitoring, periodic inspections by our techniciansand driver checks at the time of each delivery. Our monitoring programs often allow us to preventfuture problems from developing. In the rare event a problem does occur, our knowledge of the supplysystem and our experience diagnosing and alleviating issues with the supply system will allow us toquickly return service.

Supply System Overview

1

Praxair has four cryogenic supply systems (Figure 1) that are made available to customers for argon,hydrogen, nitrogen, and oxygen.

The primary components of the cryogenic supply systems are designed to meet customer flow, pressureand purity requirements. The entire system is designed to maintain consistent product pressure and purity.The primary components include:

Cryogenic storage vessels sized to meet customer-stated requirements.

Vaporizers convert cryogenic liquid to near ambient temperature gas and are sized for peak flow requirements.

Safety Systems engineered to prevent over-pressure or low-temperature hazards.

Storage Vessel

Pressure Relief System

Figure 1: Overview of a Cryogenic Supply System

Liquid toVaporizer

ProductVaporization

Pipeline PressureRegulation and Low TemperatureProtection

Gas Productto CustomerPipeline

ContentsGauge orTracker

Tank Pressure Gauge

Tank Pressure Control System

Fill Valves

Cryogenic Storage Vessel

Tanks are used to store product and are specificallydesigned for cryogenic liquids. The vessels are a tankwithin a tank (Figure 2). The inner vessel contains theproduct and is American Society of Mechanical Engineers(ASME) coded and made from nine percent nickel carbonsteel, stainless steel or aluminum. The space between theinner and outer vessels is filled with insulation and is underhigh vacuum to minimize heat transfer to the stored product.

Praxairs standard tanks range in size from 500 to 13,000gallons for argon, nitrogen and oxygen. Hydrogen tanksrange in size from 1,500 to 18,000 gallons. Each tank hasa mechanical contents gauge or an electronic Trackerdevice. These devices provide a visual indication of thetank level and are affected by many physical attributes.

The tanks have a full trycock, which is the only acceptableindicator for a full tank (i.e., a contents gauge is not anacceptable indicator). The full trycock valve is a physicallyfixed device set at the proper fill level. Transport driversare instructed to open the full trycock at the correct timeand keep it open during the remainder of the fill process.The driver terminates the fill when the trailer is empty orliquid begins to flow out of the full trycock valve.

As the full trycock valve body warms up and expands toits normal size, it may develop a small hiss. If this happens,call 1-800-PRAXAIR.

Product Fill Valve

Two main fill valves (Figure 3) are located directly in front of thecryogenic vessel and are labeled as gas and liquid. The gas fillvalve connects to the top of the tank and allows filling into the gasphase. The liquid fill valve connects to the bottom of the tank andallows filling into the liquid phase.

A Praxair driver connects the product delivery hose to the CompressedGas Association (CGA) fill connection to deliver the product. Thedriver maintains correct tank pressure by filling into the appropriategas or liquid phase.

Vacuum Space (Not to Scale)

GAS

LIQUID

Economizer Circuit(Gas Withdrawal)

LiquidWithdrawal

Valve

Pressure Regulator

Contents Gauge

Flow Direction

Pressure Building Coil

PressureReliefSystem

Fill Trycock Valves

ContentsSystem

PressureBuildingCircuit

Product To Vaporizersand Customer Pipeline

2

Figure 2: Cryogenic Storage Vessel

Figure 3: Fill Zone

CGA FillConnection

Gas Fill Valve Liquid Fill Valve

Piping to CGAFill Connection

3Tank Contents Monitoring System

Tank product level is measured with a contents gauge (Figure 4) orthe Tracker remote telemetry unit. The contents gauge and theTracker system determine the liquid level of the tank by measuringdifferential pressure between the top and bottom of the tank. Thecontents gauge is visually read. The Tracker unit can be visually readbut also automatically transmits liquid levels to Praxairs NorthAmerican Logistics Center in Tonawanda, NY.

There is a pressure gauge mounted near the contents gauge or Trackerunit that measures the gas pressure in the tank. Some pressure gaugesmay be liquid-filled and leak when damaged. If this happens, call1-800-PRAXAIR.

Figure 4: Contents Gauge

When the contents gauge and the Tracker unit are both installedon the same tank, it is normal for the readings on the two units tovary slightly because each has a different level of accuracy.

Tracker Units

There are two main types of Tracker units: wired and wireless. Wired unitscommunicate over a dedicated analog phone line and require a 110 V powersupply. Wireless units communicate via cellular communications and are poweredby a battery, which is charged from a solar panel or a 110 V power supply.

Regardless of the type of unit used, it allows Praxairs Logistics Center toforecast when to schedule deliveries.

TankPressure Gauge

BartonGauge

Liquid Side(High)

Gas Side(Low)

4TrackerTM System Readings

The four common types of Tracker units are:

Wired Unit 1 Wireless Unit 1

Wired Unit 2 Wireless Unit 2

The following information describes how to obtain readings from each unit.Wired Unit 1 (Figure 5) is a multi-channeled device that constantlyscrolls through all active channels by first displaying the channel number(e.g., -1-) followed by the corresponding reading (e.g., 0186). To acquirea reading, wait for the appropriate channel to display. This unit is alwayspowered; therefore displayed readings are always current.

Figure 5: Wired Unit 1

Wired Unit 2 (Figure 6) is a multi-channeled unit with one buttonon the bottom side of the unit. When in the correct display mode, thisdevice scrolls through all active channels. If the readings are notautomatically cycling, momentarily press the button. The unit shouldenter into the correct display mode and readings will start toautomatically cycle.

Figure 6: Wired Unit 2

Wireless Unit 1 (Figure 7) has two buttons on the displayscreen, [FILL] and [MODE]. To acquire a tank level reading onthis unit, press and hold [FILL] until display reads FILL.

The display of the unit can have a static reading for up to anhour; therefore, always press [FILL] to ensure a current reading.

Figure 7: Wireless Unit 1

Wireless Unit 2 (Figure 8) has one button located either on the top ofthe unit or on the side of the solar panel support. To turn the unit on,press and hold the button for three seconds, and then release. After theunit is powered up, it scrolls through the different readings. The tanklevel should read with inches of water column (INH2O) displayedbelow the reading.Figure 8: Wireless Unit 2

5Tank pressure decreases as product is used. When thisoccurs, to increase tank pressure:

1. The pressure-building regulator opens.

2. The liquid is withdrawn from the tank.

3. The liquid is vaporized in the pressure-building vaporizer.

4. The resulting gas is sent to the top of the tank, increasing the tank pressure.

During low-product usage, tank pressure may increaseabove the desired level. This is a result of heat transfer tothe stored product.

When the product is being used, the economizer circuit canlower tank pressure and supply gas phase product directlyto the pipeline. The economizer is only effective if productis being drawn from the system.

The system is comprised of a diverter valve and two parallelpressure relief paths (one active and the other is in reserve).Each path includes a pressure relief valve and bursting disc.The pressure relief valve opens at the tanks maximumallowable working pressure (MAWP, which is on the orderservice decal) and safely vents gas to the atmosphere. Thisvalve closes after relieving excess pressure. Sometimes thevalve does not reset and causes the gas to vent and ice to buildup around the valve.

If the pressure relief valve fails to open, the bursting discruptures to release excess pressure. When this occurs, youmay hear gas venting and see a vapor cloud as the pressuredrops to zero. If the pressure relief valve sticks open or thebursting disc ruptures, call 1-800-PRAXAIR.

Figure 10: Pressure Relief System

Figure 9: Tank Pressure Control System

The pressure relief system (Figure 10) protects the tankfrom over-pressurization. Praxair installs a dual reliefsystem to enhance reliability.

EconomizerRegulator

Tank PressureBuilding Regulator

Tank Pressure Building Coil

Tank Pressure Building Coil

The tank pressure control system (Figure 9) iscomprised of a pressure-building circuit and aneconomizer circuit.

Tank Pressure Control System

Pressure Relief SystemPressureRelief Valve

DiverterValve Bursting

Disc

6Atmospheric vaporizers (Figure 11) exchange heat with ambient air,and do not require external power. Steam or electrically heatedvaporizers are sometimes used in high-flow applications. Liquidproduct flows from the tank through the vaporizer where it is heatedand converted to a gas.

Vaporizers are sized to match customer flow requirements to avoidlow-temperature gas from entering the product pipeline. Ice on avaporizer is normal as cold cryogenic liquid condenses and freezesmoisture in the air. The greater the moisture content in the air or productuse rate, the greater the potential for ice buildup. Normally, one-halfto two-thirds of the aluminum fins of an atmospheric vaporizer arecovered with ice. If more than three quarters are covered, your flowrate may be approaching the vaporizers rated capacity.

Figure 11: Atmospheric Vaporizers

Vaporizers

Low-Temperature Pipeline Protection System

A low-temperature pipeline protection system is installed downstreamof the vaporizers to protect the customer pipeline from exposure to lowtemperatures (less than -40F).

Pipeline Product Pressure Regulation

The pipeline product pressure regulator maintains pipeline pressure within aset range. If the setpoint of the regulator occasionally drifts and causes a lowor high-output pressure, contact 1-800-PRAXAIR to correct the problem.

7

This information is not applicable for Medical SupplySystems or NFPA 86 Systems.

Low-temperature conditions can result from insufficient vaporizer capacity.Praxair uses many types of low-temperature pipeline protection systemsdepending on customer need, flow rate and pressure requirements. Thesesystems are designed to limit, reduce or shut off when product usageexceeds the vaporizer capacity. Also, weather conditions can affect thetemperature of the pipeline. Contact 1-800-PRAXAIR to evaluate siteconditions and determine if an upgrade or modification is necessary.

Main Tank and Vaporizers

The main tank is the larger of the two tanks from which product to the system is normallysupplied. The main tank normally has its own set of vaporizers (usually atmospheric) forconverting product from liquid to gas.

Medical Gas Systems

There are many differences between astandard cryogenic system and a medicalgas system (Figure 12). Although thesystem components operate the same as astandard cryogenic system, additionalequipment is added to improve thereliability and comply with necessaryindustry codes.

8

Figure 12: Medical Gas System

Reserve System

The reserve system for the medical gas system provides a secondary source of productwhen the primary source (Main System) is not functioning. The reserve system isdesigned to operate when the main system fails so product is rarely drawn from thereserve system.

Usually the reserve system is a smaller liquid tank with its own vaporizers that providesproduct flow to the system when the main tank runs empty or malfunctions. In some cases,where the normal use rate is very low the reserve system may be a cylinder bank. Praxairdelivery drivers monitor the reserve system, and fill as necessary. Although code requires aminimum of a 24-hour reserve system supply, Praxair normally provides a reserve systemthat exceeds 24 hours.

The Praxair medical gas system is designed to utilize the gaseous product from thereserve system that would otherwise be vented by feeding this product into the productuse line. This keeps the tank pressure at the desired level to prevent loss of product.

It is possible for the product in the reserve system to be consumed and potentially trigger an alarm (low reserve level) even though the system is properly functioning.

Alarm Probable Cause

Alarm System

The system includes a series of alarms that are required by code. These alarms allow you to monitorthe condition of the system and be alerted when abnormal conditions occur. An alarm annunciator isrequired inside a medical facility at a location where it is monitored at all times. The alarms andconditions are listed in Table 1. If you experience any alarms, contact Praxair at 1-800-PRAXAIR.

Action

Main Tank Low Level Tank has reached the low level point

Gauge / TrackerTM device malfunction

Check the tank level

Verify/schedule delivery or service

Reserve In Use System switched over to theReserve System

Main tank is empty

Main tank malfunctioned

Reserve System or alarmmalfunctioned

Check tank levels and pressure inboth main and reserve tanks

Verify/schedule delivery or service

Reserve Tank Low Level Reserve System reached a remaining supply of 24 hours

Gauge / Tracker device malfunctioned

Alarm malfunctioned

Check tank level

Verify/schedule delivery or service

Low Reserve Pressure The Reserve System is about to runempty. take immediate action

Alarm malfunction

Check the reserve and main tanklevels and pressure. If the alarm isvalid, take immediate action

Verify/schedule delivery or service

Abnormal Line Pressure orHigh/Low Line Pressure

Facility line pressure (use pressure)dropped to 20 percent below thenormal pressure or rose 20 percentabove the normal pressure

Alarm malfunction (medical facilityresponsibility)

Check the reserve and main tanklevels and pressure

Check the line pressure

Arrange for service/repair

9

Table 1: Medical Facility Alarm System

10

Figure 13: Order Information Decal

Item Name Description

ORDER LEVEL Dynamic and changes with use rates(may or may not be on decal)

TANK FILLS AT Level at which the tank is full, and varies as the densityof the cryogenic liquid changes

DRIVER MAINTAIN PRESSURE AT The pressure the driver is to maintain while filling

TANK M.A.W.P. Maximum allowable working pressure by design andindustry code

PIPELINE PRESSURE Pressure of the pipeline

Pressure at which pressure-building circuit activates

ECONOMIZER SET AT Pressure at which economizer is set to activate

FILL SYSTEM TYPE Informs the truck driver how to fill the tank

INSPECTION DATE Date of last unit inspection

Order Information

Every Praxair cryogenic supply system has several information decals attached to the unit. Theorder information decal (Figure 13) provides valuable information to the customer, driver andtechnician. Table 2 explains each decal item.

ORDER LEVEL:

TANK FILLS AT:

DRIVER MAINTAIN PRESSURE AT:

TANK M.A.W.P:

Order level is dynamicand changes with use rate.

INCHES

INCHES

PSIG

PSIG

A, B, C, or DFILL SYSTEM TYPE:

A: SEPARATE LIQUID & GAS FILL VALVESB: DIVERTER FILL VALVE

C: LIQUID FILL VALVE ONLYD: GAS FILL VALVE ONLY

PIPELINE PRESSURE:

PRESSURE BUILDER SET AT:

ECONOMIZER SET AT:

INSPECTION DATE:

PSIG

PSIG

PSIG

PX2553D

Gauge Readings & Product Orders24 HoursCall 1-800-621-7100

For 24 Hour ServiceCall 1-800-PRAXAIR (772-9247)E-mail Inquiries to info@praxair.com

Table 2: Information Decal

PRESSURE BUILDER SET AT

Copyright 2010 Praxair Technology, Inc.All rights reserved

Praxair, the Flowing Airstream design, Trackerand Making our planet more productive, aretrademarks or registered trademarks ofPraxair Technology, Inc. in the United Statesand/or other countries.

The information contained herein is offeredfor use by technically qualified personnel attheir discretion and risk without warranty ofany kind.

Printed in the United States of America09/10

P-7896D

Praxair, Inc.39 Old Ridgebury RoadDanbury, CT 06810-5113USA

www.praxair.cominfo@praxair.com

Telephone:1-800-PRAXAIR (1-800-772-9247)(716) 879-4077

Fax:1-800-772-9985(716) 879-2040